Asa Grey was born, raised, and educated in upstate New York. Like many botanists of that time he was trained as a physician. Dr. Gray practiced medicine for only a few years before his consuming interest in plants compelled him to switch careers and become an understudy of the New York botanist Dr. John Torrey (Torreya californica). Gray soon advanced from being Torreys protégé to his collaborator in their epic work The Flora of North America. Their collaboration made two major advances for American botany. One was the shifted from using the outdated and artificial Linnaean system of classification to a natural (phylogeneticaly based) system modeled on that of A. L. de Jussieu and A. P. de Candolle. They also established the practice of basing the taxonomy of American plants on the type specimens. Gray also wrote the still-useful, Grays Manual of Botany, a flora of north eastern North America. In his phytogeographic research, Gray explained that many of the plant taxa which appeared in both eastern Asia and eastern North America, are not separate creations but rather, descendants from a Tertiary circum-boreal flora that was pushed southward by the Pleistocene glaciation.
In 1842 Dr. Gray accepted the Fischer professorship of natural history at Harvard University. This professorship made him, at the time, the only adequately supported professional botanist in the United States. He continued his botanical studies at Harvard until 1887, fifteen years after his formal retirement. Dr. Grays teaching skills apparently fell far short of his taxonomic skills. None of his students, in his thirty-odd years at Harvard, ever made a name for themselves.
In matters of nomenclature and taxonomy Gray dominated the field of botany like no American botanist before or after him. Gray had an intuitive knack for taxonomy. Many of the species he described were good species (real) that have withstood the test of time. Asa Gray described and elaborated upon many of the botanical discoveries that were brought back from the numerous expeditions of the American territories during the mid-1800s. Gray actually did little collecting in the American West, but many of the plant collections from the western expeditions were sent to him to examine. Consequently, in the Jepson Manual you will see A. Gray after the hundreds of species names that he authored.
Asa Gray was the first American botanist to have an international reputation. He made five extended European journeys where he did research and hobnobbed with Europes major botanists of the era, including Charles Darwin and Joseph Dalton Hooker. He was one of the only people that Darwin kept fully informed regarding his publication of The Origin of Species. Gray was Americas foremost proponent and defender of Charles Darwin and his theories on evolution. His collective essays on the subject were compiled in a book Darwiniana (1876).
No one has dominated the American botanical scene like Asa Gray. In all, Asa Gray produced a phenomenal 780 publications. He started the Harvard Herbarium, which now holds 4,600,000 specimens, making it the second largest herbarium in the USA and the eighth largest in the world. As a fitting testament to his prolific output; Harvard University hired four botanists to replace him when he died in 1888.